1. (Field of the Invention)
The present invention generally relates to a continuous fastener carrier for use with an automatic fastening machine and, more particularly, to a fastener carrier comprising a carrier strip having fasteners removably mounted on the carrier strip in at least one row over the length of such a carrier strip.
The present invention also relates to a fastening method for driving a fastening member, which method can be practiced with the use of the continuous fastener carrier of the type referred to above having at least one row of fastening members removably mounted on the carrier strip.
2. (Description of the Prior Art)
An automatic fastening machine is currently widely used in industries that manufacture structural elements by driving fastening members such as, for example, screws, bolts or rivets onto the structural elements. In general, when the products manufactured are compact and light-weight, the automatic fastening machine handles relatively small screw members. The automatic fastening machine currently available for driving screw members onto small, or miniature, structural elements comprises a pneumatic or electric screw driver and a supply unit including a hopper for accommodating therein a mass of screw members and a chute for guiding the screw members one by one towards the screw driver.
A specific example of the prior art automatic fastening machine operable with screw members each having a head and an externally threaded stem will now be discussed with particular reference to FIGS. 15 to 17 of the accompanying drawings.
Referring first to FIG. 15 illustrating the supply unit in a schematic side sectional view, the hopper and the chute are generally identified by 100 and 101, respectively. The hopper 100 is used to accommodate therein a mass of screw members each having a head and an externally threaded stem and has a slot defined generally at the bottom thereof. The chute 101 is a generally elongated bar having a guide groove 102 defined therein so as to extend axially from one end to the opposite end thereof and having one end protruding into and rigidly secured to the hopper 100. The chute 101 is inclined downwardly from the hopper 100 with its opposite end operatively associated with the screw driver as will be described later.
For enabling some of the screw members within the hopper 100 to be scooped upwardly and then transferred onto the chute 101, a generally sector-shaped scraper 103 is employed. This scraper 103 is adapted to be driven by an electric motor 104 for pivotal movement between raised and lowered positions about a bearing pin 105 and is formed at 106 with a groove which is, when the scraper 103 is moved to the raised position as shown in FIG. 16, brought into alignment with the groove 102 in the chute 101. This scraper 103, regardless of the position thereof, closes the slot defined at the bottom of the hopper and, therefore, there is no possibility of some of the screw members falling out of the hopper 100 through the slot.
The chute 101 also has an overhead bar 107 extending immediately above and in alignment with the guide groove 102 in the chute 101 and spaced therefrom a distance corresponding to the thickness of each of the heads of the screw members such that each of the screw members being slid along the chute 101 will not separate from the guide groove 102. A gating member 108 is secured to one end of the overhead bar 107 adjacent the hopper 100 for ejecting back into the hopper 100 the screw members which are transferred onto the chute 101 with the wrong orientation as will be described later.
The supply unit having the structure described hereinabove operates in the following manner. Assuming that the scraper 103 is in the lowered position as shown in FIG. 15, when the motor 104 is driven, the scraper 103 pivots about the bearing pin 105 from the lowered position towards the raised position with some of the screw members being scooped upwardly by the scraper 103. Some of those screw members so scooped upwardly by the scraper 103 may have their stems received in the groove 106 as indicated by X in FIG. 16 and some of them may have their stems oriented upwardly as indicated by Y in FIG. 16. As the scraper 103 approaches the raised position, the screw members so scooped start sliding along the groove 106 and, as soon as the scraper 103 arrives at the raised position shown in FIG. 16, the screw members sliding downwards along the groove 106 are successively transferred onto the chute 101 with their stems received in the groove 102 in the chute 101.
However, the gating member 108 permits the passage thereunder of only the screw members having the proper orientation, that is, the screw members X having their stems received in the groove 106, and ejects from the scraper 103 the screw members having the wrong orientation, that is, the screw members Y having their stems not received in the groove 106.
The supply unit used in the prior art fastening machine has problems in that, when each of the screw members handled thereby is of a type in which the stem has a relatively small length as compared with the outer diameter thereof, the screw members will not be correctly received in the groove 106 in the scraper 103 because this type of screw member generally has a center of gravity lying in the head and that. Where each of the screw members handled thereby is of a type in which the stem has a relatively small outer diameter, the screw members can hardly be received in the groove 106 in the scraper 103. Moreover, since the exact alignment between the groove 106 in the scraper 103 and the groove 102 in the chute 101 at the transition point between the scraper 103 and the chute 101 is difficult to achieve, a smooth transfer of the screw members from the scraper 103 onto the chute 101 cannot be achieved.
The screw driver used in the prior art fastening machine is best illustrated in FIG. 17 and comprises a vacuum sleeve 109 communication in any suitable manner with a source of substantial vacuum and having a screwing bit 110 accommodated therein for axially sliding relative to the sleeve 109. This screw driver is supported for movement up and down between a raised position, shown by the solid line, and a lowered position shown by the phantom line, past a screw receiving station at which the screw member is caught by the screw driver with its head sucked onto the sleeve 109.
At the screw receiving station, a generally U-shaped screw holder 111 is disposed and rotatably mounted on a support shaft 112 for pivotal movement about such support shaft 112 between a receiving position, shown by the solid line, and a release position shown by the phantom line. However, the screw holder 111 is normally biased to the receiving position by the action of a torsion spring 113 mounted on the bearing shaft 112. This screw holder 111 has a groove defined therein having a width identical to that of the groove 102 in the chute 101 and is positioned in the vicinity of the end of the chute 101 that is remote from the hopper 100 (FIGS. 15 and 16) so that each of the screw members transferred through the chute 101 can fall by gravity onto the screw holder 111 with the respective stem received in the groove in the screw holder 111 as shown by Xa. The other screw members following the screw member which has been transferred onto the screw holder 111 in the manner as hereinabove described are retained on the chute 101 by the action of an escapement 114 supported by the chute 101 for pivotal movement between a blocking position, as shown by the solid line, and a retracted position. This escapement 114 is operable to permit the screw members on the chute 101 to be successively delivered onto the screw holder 111 one at a time while reciprocally pivoting between the blocking and retracted positions.
The screw driver operates in the following manner. Assuming that one screw member Xa has been delivered onto the screw holder 111 while the latter is in the receiving position, the screwing bit 110 is lowered together with the sleeve 109. During the lowering of the screw driver, the lower end of the sleeve 109 is brought into contact with the head of the screw member Xa, thereby holding the screw member Xa under suction. The continued lowering of the screw driver causes the screw holder 111 to pivot against the torsion spring 113 from the receiving position towards the release position, while allowing the screw member Xa to leave the groove in the screw holder 111. Shortly before or simultaneously with the arrival of the sleeve 109 at the lowered position shown by the phantom line, the screwing bit 110 is lowered while being driven about its longitudinal axis so that the screw member can be eventually driven or threaded into a structural element by the screwing bit 110.
After the completion of the fastening operation, both the sleeve 109 and the screwing bit 110 are elevated towards the raised position in readiness for the next succeeding cycle of the fastening operation.
The screw driver used in the prior art fastening machine has problems in that, when each of the screw members handled thereby is of a type in which the stem has a relatively small length as compared with the outer diameter thereof, the screw members tend to be upset during the delivery thereof from the chute 101 onto the screw holder 111 because this type of screw member generally has a center of gravity lying in the head and in that, when each of the screw members handled thereby is of a type in which the stem has a relatively small outer diameter, not only can the screw members riding on the chute 101 hardly be separated one by one by the action of the escapement 114, but also each screw member delivered onto the screw holder 111 tends to be so instable as to cause the vacuum sleeve 109 to fail to hold the screw member properly.
Apart from the above-discussed prior art screw driver, another version is well known which employs a screw feed sleeve having a branch pipe offset laterally from the feed sleeve. The branch pipe is coupled through a flexible tubing and then through the escapement assembly with a source of screw members which may, for example, be a hopper having a structure as shown in and described with reference to FIGS. 15 and 16.